Vehicles equipped with an electric motor to transfer drive torque to the driven wheels are becoming increasingly desirable by a greater number of users than ever before. One of the most prominent benefits of electric vehicle use includes eliminating undesirable emissions exhausted by an internal combustion engine. Furthermore, battery technology has sufficiently developed such that a reasonably sized battery pack may output enough energy to drive the electric motor and meet driver's needs for acceleration and range. To provide a usable vehicle in the field, the battery pack must also be efficiently charged and discharged many times.
One challenge facing electric vehicle designers includes the sensitivity of the electric vehicle batteries to temperature. More specifically, the maximum charge current and the maximum discharge current of the batteries vary based on battery temperature, among other things. The temperature of the battery may vary during operation due to chemical reactions taking place within the battery as well as the ambient temperature of the environment in which the vehicle is positioned. For example, the maximum charging current of a battery may be significantly reduced when the temperature of the battery is below a predetermined limit. Battery charging and discharging efficiency may also be less than optimal when the temperature of the battery is above a predetermined operating limit.
Furthermore, existing heaters for vehicle engines may not be suited to warm an electric vehicle battery pack. Many existing engine block heaters are energized by a 12v or 24v power supply. The watt-density of the heating element is defined accordingly. While these heaters perform a desired function, they may not be simply installed within an electric vehicle equipped with a high voltage power supply in the range of 450 Vdc. Controlling the heaters associated with the high voltage circuit also becomes very important to assure that an overheating condition is avoided. Therefore, it may be beneficial to provide a temperature control system to maintain a desired electric vehicle battery temperature.